The applicant discloses a posture control system of a legged mobile robot, for mobile robots, in Japanese Laid-Open Patent Application No. Hei 10 (1998)-230485. In this prior art, it is configured to displace the position of the center of gravity of the robot by correcting a posture gradually over a long period of time to displace a body of the robot so as to generate a moment of gravity for compensation, so as to maintain or preserve the dynamic balance, in particular the equilibrium that balances robot posture dynamically, when the robot receives an unexpected reaction force from an object. At the same time it is configured, during a transient period, to preserve the dynamic balance by driving a foot to move to take a posture to brace legs, so as to generate a total floor reaction force's moment for compensation about a desired floor reaction force central point (that is equal to a desired ZMP).
Thus, in the aforesaid prior art, if unexpected reaction force acting from the object changes abruptly, at that moment (in a short period of time), the robot is operated to move the foot to brace legs in order to maintain or preserve the dynamic balance. That is to say, the prior art ensures to stabilize the posture by generating the total floor reaction force's moment.
Further, the applicant proposes a technique (in Japanese Laid-Open Patent Application No. Hei 10 (1998)-277969) to generate a moment as a total floor reaction force's moment actively to restore a posture of the robot when the posture is tilted or inclined, regardless of whether the robot receives a reaction force from the object. However, since the total floor reaction force's moment generated by the aforesaid technique has a limit, if trying to generate the total floor reaction force's moment beyond the limit, a part of a foot may be lifted up, resulting in the robot losing the dynamic balance or, at worst, tipping over.
Furthermore, the applicant also proposes a technique to maintain the dynamic balance by correcting a body trajectory of a robot, instead of generating a total floor reaction force's moment (in Japanese Patent No. 3269852). In the prior art, however, since a foot landing position, etc., is needed to be corrected, if the robot is controlled to work with the object by using the arm, the body or foot may sometimes be likely move from an appropriate position for working.
In addition, in the case that the robot is controlled to work to impart some motion to an object, in order to accomplish a task as expected, it is preferable not to influence on a motion of the object, when a control to maintain the dynamic balance or to restore a tilted or inclined posture of the robot is implemented.